The invention relates to an electrical device, in particular a power tool, equipped with a commutator motor, and also relates to an accessory for an electrical device.
In electric generators with commutator motors (universal or direct current motors), the commutator transmits current to the armature winding of the electric motor. To this end, carbon brushes slide with a certain contact pressure over the laminated contact roller of the commutator, which is connected to the armature shaft of the electric motor and whose plates are electrically insulated from one another and are non-rotatably connected to the armature shaft.
The carbon brushes and commutator used experience wear due the constant friction. Over time, this leads to a narrowing of the commutator that becomes more pronounced as time goes on. As a rule, it is not easily possible to replace the commutator since it is affixed to the armature shaft; by contrast, it is generally easy to replace carbon brushes, particularly in high-quality electrical devices.
In the optimum case, the replacement carbon brushes are provided with a lateral beveling or rounding so that a contact between the replacement carbon brushes and the narrowed commutator over the greatest possible area is achieved in the shortest possible break-in period. However, carbon brushes without a corresponding contouring are also available on the market. If such replacement carbon brushes are used, as a rule, only very small, usually linear, contact surfaces are produced between the replacement carbon brushes and the commutator. This results in a very high local energy density since all of the current must flow through the small carbon contact surfaces. This in turn results in a highly elevated local temperature, which can have negative consequences for the service life of the commutator and carbon brushes. In addition to the high energy density, the minimal contact surfaces also result in a high mechanical stress. In particular, the laminated commutator grinds away a very large quantity of carbon from the carbon brushes within a very short time, which generates an increased amount of carbon dust. Among other places, this carbon dust collects between the plates of the collector, which can produce an electrical bridge between the plates and therefore lead to a failure of the electrical device.